As uses of RF transceiving technologies proliferate, so does the likelihood of potentially performance degrading interference being received by a RF transceiver, such as an automotive radar system. Possible effects include reduced ability of the RF receiver to detect objects of interest and/or to estimate relevant parameter values of those detected objects, such as object range, object bearing, and/or object Doppler. The reliable detection of degrading interference becomes especially important for safety-critical applications. For example, a radar mounted in the front bumper of a vehicle may be relied upon to detect objects in the path of the host vehicle. If the radar cannot perform its function within specifications due to the presence of interference, then it must notify the controlling system of this situation so that it can recover to a safe state.
Interference may be categorized in several ways, such as continuous versus intermittent, narrowband versus wideband, etc. Narrowband interferers may include AM radio broadcasts and amateur radio signals. Wideband noise that extends across a large portion of the RF spectrum may also interfere. Wideband noise can be caused, for example, by electrical machinery, internal combustion engines (e.g., lawn mowers), fluorescent lights, and other sensors. Wideband interferers can be somewhat random, and may be more difficult to avoid. The bandwidth of a RF receiver can be approximated by the inverse of its receiver gate. For example, the bandwidth of a radar receiver having receiver gate of 400 ns is 2.5 MHz. An example of a wideband interference source is the RF transmission of a narrow pulse, such as having a duration of 10 ns, which would have a bandwidth of 100 MHz. Another example of a wideband interference source is a fast frequency chirp, such as continuous wave (CW) transmission that changes frequency in steps or continuously over a span of 200 MHz over a duration of 10 μsec.
All RF receivers experience electrical fluctuations produced by internal components, which is known as thermal noise. The thermal noise and a desired signal of interest (SOI), such as a reflection from a target object of a RF signal transmitted by the sensor, undergo subsequent amplification. The thermal noise may change with temperature, component aging and/or be inherently distinct for different radar systems.
A significant challenge is to distinguish between the presence of degrading interference and ordinary changes in thermal noise contributions. The latter may be caused by changes in receiver-chain amplification, which affects the signal and noise equally, thereby not presenting a significant change in receiver functionality. The former, however, causes a significant increase in receiver noise levels without the corresponding improvement in signal quality, therefore degrading the ability of the receiver to perform its intended function.
Current technologies might attempt to solve this interference differentiation problem by estimating the thermal noise level of the receiver. The presence of interference would be declared when the receiver noise level exceeds some threshold above the estimated thermal noise level. For example, interference might be declared when the receiver noise consistently exceeds 10 dB above the estimated thermal noise level. This technique, however, does not always provide good results, due to the challenge of accurately estimating the thermal noise level of the receiver. In practical receivers, there can be significant variability in receiver-chain gain due to changes in temperature, component aging and/or between different instances of manufactured radars. It is often beyond state-of-the-art and/or available resources to adequately characterize and model the gain in order to adequately predict thermal noise levels.
The direct measurement of thermal noise level by the receiver is another possible technique. The implementation of this technique, however, may require the presence of additional and costly receiver circuitry. It may also require the interruption of normal radar functionality in order to perform this measurement, which might be undesirable.
Poor estimation of thermal noise levels can cause excessive false detections of interference. This might be remedied by raising the detection threshold, for example, from 10 dB to 25 dB. A higher threshold, however, degrades the ability to detect the presence of lower, yet still significantly degrading, levels of interference in the radar receiver. To achieve very low false-detection rates, the threshold might even need to be increased to such a high level that degrading interference can usually not be discriminated.
Therefore, there is a need for a RF interference detector and method with improved identification of system performance degrading interference.